The key player in prokaryotic transcription termination is the ρ (rho) factor.

• ρ–dependent termination

– Rho is an RNA-helicase that binds a rut site on the nascent mRNA.

– It moves along the transcript, catches up with RNA polymerase and unwinds the RNA–DNA hybrid, releasing the mRNA.

By contrast:

• σ (sigma) is needed for initiation, not termination.

• α and γ are subunits of RNA polymerase (α for assembly/stability, γ isn’t a termination factor).

Answer: Option A (ρ)